The present invention relates to a method and apparatus for producing a useful soil product from waste products, such as petroleum contaminated soil and sedimentary sludge.
The effective cleanup and disposal of soils which are contaminated with petroleum products and other contaminants have recently become major environmental concerns. As one specific example of the problem, a large number of underground fuel tanks have been found to be leaking and releasing a variety of contaminants into the surrounding soil, and as these tanks are being removed and repaired pursuant to environmental regulations, the volume of contaminated soil has been growing. Many communities no longer permit such soil to be placed in landfills, and thus a need exists for the decontamination of the soils.
Co-pending U.S. patent application Ser. No. 07/565,945, now U.S. Pat. No. 5,176,445, discloses a prior soil decontamination apparatus wherein the soil is initially heated to a relatively low temperature in a rotary dryer so as to volatilize the contaminants, and the volatilized contaminants are then fed to a high temperature after burner which converts the volatile contaminants to non-toxic products which are then filtered and released to the atmosphere. This process also produces clean, purified soil at high temperatures, and this hot, dry soil must be cooled and moisture added before it can be safely handled without producing excessive dust. Since most organic matter has been removed from this soil, it will not support plant life, and it therefore is normally used as roadbase fill and cover for landfills where its infertile characteristics can be tolerated.
The effective disposal of sedimentary sludge produced by municipal sewage treatment systems also presents an environmental concern. Huge quantities of such sludge are produced by municipalities, for example, a municipality of 300,000 people produces about 75,000 to 80,000 wet tons per year. Filtering presses and other devices are used to reduce the moisture in such sludge to about 65%, but efforts to further reduce the moisture content, as by using heat to dry the sludge, have not been practical because of the cost, odor and air pollution.
Sedimentary sludge also contains many disease producing organisms, and the potential exists for these organisms to be spread by a sludge which has not been pasteurized or sterilized. Such treatment is not normally cost effective, and therefore, it is common for sludge to be simply placed in land fills without treatment.
It is accordingly, an object of the present invention to provide a method and apparatus for effectively and economically decontaminating petroleum contaminated soils and the like.
It is another object of the present invention to provide a method and apparatus for the effective and economical use of sedimentary sludge.
It is a further object of the present invention to provide a method and apparatus for effectively decontaminating contaminated soil, while concurrently sterilizing sedimentary sludge, and which utilizes the products of each process to promote the efficiency of the overall process, and which produces a useful soil product.